A wide variety of different wireless data technologies now exist, some in direct competition with one another, others designed to be optimal for specific applications. Wireless technologies can be evaluated by a variety of different metrics. Generally, these can be grouped as follows:
UWB, Bluetooth, ZigBee, and Wireless USB are intended for use as so-called Wireless PAN systems. They are intended for short-range communication between devices typically controlled by a single person. A keyboard might communicate with a computer, or a mobile phone with a hands-free kit, using any of these technologies.
The ZigBee set of high-level communication protocols is based upon the specification produced by the IEEE 802.15.4 task group.
IEEE 802.15 is the 15th working group of the IEEE 802 which specializes in Wireless PAN (Personal Area Network) standards. It includes five task groups (numbered from 1 to 5). IEEE 802.15.4-2003 (Low Rate WPAN) deals with low data rate but very long battery life (months or even years) and very low complexity. The first edition of the 802.15.4 standard was released in May 2003. In March 2004, after forming Task Group 4b, task group 4 put itself in hibernation.
Mesh Networking
Mesh networking is a way to route data, voice and instructions between nodes. It allows for continuous connections and reconfiguration around broken or blocked paths by “hopping” from node to node until the destination is reached. A mesh network whose nodes are all connected to each other is a fully connected network. Mesh networks differ from other networks in that the component parts can all connect to each other via multiple hops, and they generally are not mobile. Mesh networks can be seen as one type of ad hoc network. Mobile ad-hoc networking (MANet), and mesh networking are therefore closely related, but mobile ad hoc networks also have to deal with the problems introduced by the mobility of the nodes.
Mesh networks are self-healing: the network can still operate even when a node breaks down or a connection goes bad. As a result, a very reliable network is formed. This concept is applicable to wireless networks, wired networks, and software interaction.
A wireless mesh network is a mesh network implemented over a wireless network system such as wireless LAN.
Mesh networks may involve either fixed or mobile devices. The solutions are as diverse as communications in difficult environments such as emergency situations, tunnels and oilrigs to battlefield surveillance and high speed mobile video applications on board public transport or real time racing car telemetry.
The principle is similar to the way packets travel around the wired Internet—data will hop from one device to another until it reaches a given destination. Dynamic routing capabilities included in each device allow this to happen. To implement such dynamic routing capabilities, each device needs to communicate its routing information to every device it connects with, “almost in real time”. Each device then determines what to do with the data it receives—either pass it on to the next device or keep it. The routing algorithm used should attempt to always ensure that the data takes the most appropriate (fastest) route to its destination with the fewest number of transmissions down incorrect network routes/paths.
Routing Tables
In computer networking a routing table, or Routing Information Base (RIB), is an electronic table (file) or database type object that is stored in a router or a networked computer. The routing table stores the routes (and in some cases, metrics associated with those routes) to particular network destinations. This information contains the topology of the network immediately around it. The construction of routing table is the primary goal of routing protocols and static routes.
Routing tables are generally not used directly for packet forwarding in modem router architectures; instead, they are used to generate the information for a smaller forwarding table which contains only the routes which are chosen by the routing algorithm as preferred routes for packet forwarding, often in a compressed or pre-compiled format that is optimized for hardware storage and lookup.
Related Patents and Publications
U.S. Pat. No. 6,972,682 (Lareau et al., 2005), incorporated by reference herein, discloses monitoring and tracking of assets by utilizing wireless communications. Systems, devices, methods, and programs disclosed herein provide a solution for monitoring and tracking assets by utilizing wireless communications. A representative system for monitoring assets includes a remote monitoring station (RMS) and a network of identification (ID) tags. Each ID tag is coupled to an asset and is configured to wirelessly communicate with other ID tags in the network within a predetermined proximity. Each tag is also configured to relay communications from other ID tags so that a communication path is established between the RMS and any ID tag in the network, either directly or via other ID tags.
US Patent Publication 2006/0088018, incorporated by reference herein, discloses system and method for communicating over an 802.15.4 network. A method of reducing data transfer while increasing image information over an 802.15.4 network includes obtaining an image with a sensor, modulating a representation of the image using a first 802.15.4 modem, sending the representation of the image to a coordinator, demodulating the representation of the image using a second 802.15.4 modem, and digitally enhancing at least one of the representation of the image and the image. A system for communication over an 802.15.4 network includes a sensor for obtaining data, the size of the data being at least an order of magnitude greater than the size of an 802.15.4 packet, a first 802.15.4 modem coupled to the sensor, a buffer for temporarily storing the data to allow transmission of portions of the data; the buffer being coupled to the sensor, a coordinator coupled to the sensor, the coordinator being capable of communicating with a computer, and a second 802.15.4 modem coupled to the coordinator. As further disclosed therein:
This application relates generally to data communication and particularly to data communication using the wireless IEEE 802.15.4 protocol over a WPAN (wireless personal area network) optimized for low power, low data rate networks.
A brief history of the IEEE 802.15.4 protocol development begins as follows: whereas IEEE 802.11 (WiFi) was concerned with features such as Ethernet matching speed, long range (100 m), complexity to handle seamless roaming, message forwarding, and data throughput of 2-11 Mbps; WPANs (Wireless Personal Area Networks) are focused on a space around a person or object that typically extends up to 10 m in all directions. The focus of WPANs is low-cost, low power, short range, and very small size. The IEEE 802.15 working group currently defined three classes of WPANs that are differentiated by data rate, battery drain, and quality of service (QoS). The present invention concerns the last class. The first class, a high data rate WPAN (IEEE 802.15.3) is suitable for multi-media applications that require very high QoS. Medium rate WPANs (IEEE 802.15.1/Bluetooth) will handle a variety of tasks ranging from cell phones to PDA communications and have QoS suitable for voice communications. The last class, a low rate WPANs (IEEE 802.15.4/LR-WPAN) is intended to serve a set of industrial, residential, and medical applications. These applications have very low power consumption, a cost requirement not considered by the above WPANs, and relaxed needs for data rate and QoS. The low data rate enables the LR-WPAN to consume very little power.
The IEEE 802.15.4 wireless protocol is still in its infancy and is being rolled out primarily in applications such as sensors, interactive toys, smart badges, remote controls, remote metering, and home and industrial automation. The 802.15.4 protocol supports data rates of 250 kbps at 2.405-2.480 Ghz with 16 channels (worldwide), 40 kbps at 902-928 Mhz with 10 channels (Americas), and 20 kbps at 868.3 Mhz with 1 channel (Europe). The protocol supports automatic network establishment by the coordinator; a fully hand-shaked protocol for transfer reliability; and power management to ensure low power consumption. The wireless IEEE 802.15.4-2003 standard was approved in May of 2003 and was published in October of the same year. The standard is still under further development with 2 additional task groups, 802.15.4a and 802.15.4b continuing the development. Current areas of development (as of September 2005) include resolving ambiguities, reducing unnecessary complexity, increasing flexibility in security key usage, and considerations for newly available frequency allocations among others.
General requirements of sensor/control networks include that they can be quite large, employing 255 clusters of 254 nodes each (64,770 nodes); are suitable for latency-tolerant applications; can operate very reliably for years without any operator intervention; have very long battery life (up to several years from an AA cell); very low infrastructure cost (low device and setup costs); very low complexity and small size; and device data rates and QoS (Quality of Service, i.e., delay, jitter, throughput, and reliability) needs are low.
The IEEE 802.15.4 standard was developed to address the low power, low-bandwidth market; primarily focused on controls signals. In general terms, 802.15.4 is seen as one of the lowest-bandwidth wireless technologies available on the market today, and provides the corresponding benefit of long battery life. Presentations typically show the following: TABLE-US-00001 TABLE 1 Technology Range Data Rate 802.15.4 WPAN to WLAN<0.25 Mbps 802.15.1 (Bluetooth) WPAN>0.1 Mbps; <1 Mbps 802.11 (WiFi) WLAN>1 Mbps; <100 Mbps.
ZigBee is a protocol layer that sits “on top” of 802.15.4, and seeks to establish an interoperability standard for many companies to adopt, and to enable a smarter network with intelligence. ZigBee, or 802.15.4, sits below Bluetooth in terms of data rate. The operational range of ZigBee is typically stated as 10-75 m compared to 10 m for Bluetooth. ZigBee uses a basic master-slave configuration suited to static star networks of many infrequently use devices that talk via small data packets. Bluetooth's protocol is more complex since it is geared towards handling voice, images, and file transfers in ad-hoc networks. Bluetooth devices can support scatternets of multiple smaller non-synchronized networks (piconets). It only allows up to 8 slave nodes in a basic master-slave piconet set-up. ZigBee nodes spend much of their time sleeping, but the protocol is optimized for quick wake up and response. When a ZigBee node is powered down, it can wake up and get a packet in around 15 msec whereas a Bluetooth device would take around 3 sec to wake up and respond.
US Patent Publication No. 2006/0092896, incorporated by reference herein, discloses method of communication between reduced functionality devices in an IEEE 802.15.4 network. In an 802.15.4 network, each reduced functionality device (RFD) is permitted to communicate with only an assigned full function device (FFD). The present invention allows each of the RFDs to communicate with another RFD upon the RFD determining that the local FFD assigned to the RFD is inoperable or unable to communicate. Under emergency conditions, the RFD is able to communicate with closely located RFDs such that the closely located RFDs can receive and respond to an emergency situation and/or repeat the message. To satisfy the 802.15.4 standards, communication between the RFDs is allowed only during emergency conditions and when the FFD is inoperative. A comprehensive test procedure is included to insure the integrity of the system is preserved at all times as further disclosed therein.
IEEE standard 802.15.4 was developed to standardize communication between devices operating within a local area network (LAN). The IEEE standard was targeted at home, building and industrial automation and controls, consumer electronics, PC profiles and medical monitoring. The standards define the interoperability, certification testing and branding of devices that operate within the IEEE standard.
In a standard 802.15.4 network, the network includes three different device types. The first device type is classified as a network coordinator and maintains overall network knowledge.
The second type of device type in an 802.15.4 network is referred as a full function device (FFD). Each of the FFDs has full communication functionality with all the features required by the 802.15.4 standard. Further, the FFD includes additional memory and computing power that makes it ideal for acting as a network router. Each of the FFDs is able to communicate with both the network coordinator and lower level devices referred to as reduced function devices (RFDs).
The third type of device included in the 802.15.4 network is a reduced function device (RFD) that is designed to communicate with a single FFD. Each RFD includes limited functionality as specified by the 802.15.4 standard to limit the cost and complexity of the RFD. As required by the literal interpretation 802.15.4 standard, each RFD communicates solely with an FFD and cannot communicate with other RFDs.
The 802.15.4 network is contemplated as being particularly desirable in transmitting information within a building automation system. For example, each of the RFDs could be an environmental sensor, smoke detector, motion detector or any other kind of monitoring equipment that is required for monitoring and controlling the operation of a building.
Although the 802.15.4 networking configuration has worked well, a problem can occur if and when a FFD is rendered inoperative or is out of communications, such as during a power interruption. FFDs are generally designed to be online at all times and therefore are normally line powered. RFDs, by design, are not always online and typically are battery powered. When one of the FFDs is removed from the network, such as during the power loss to the FFD, the RFDs associated with the disabled FFD are unable to communicate information across the network unless they are within communication range of another FFD. If most or all of the FFDs are removed from the network (as might be the case during a power outage), then all of the RFDs will be unable to communicate a detected alarm condition. This drawback can become important when the RFDs are safety devices, such as smoke detectors.
Therefore, a need exists for an improved communication method operating within the 802.15.4 standard or any extension thereof, that allows for communication during emergency situations or when one or more of the FFDs has been rendered inoperative.
Prior wireless networks and current ZigBee implementation devices need a way to periodically check in and link up with the network to send information (events, network maps, etc.). Anytime a device is listening on the network it is at its highest power drain—conversely anytime a device is asleep it is unable to route other messages. Therein lies the problem.
ZigBee operates by having one to many FFD (Full Function Devices) that are powered from unlimited sources (AC power usually, or really big batteries) because they are up all the time. These FFDs are placed in fixed places as usually they are plugged in. Battery device RFDs usually need to be within one hop of the FFD to communicate, and need to be up listening to catch incoming setting messages. Hence the “static or limited movement” type of network.
Each of the RFD devices needs to beacon to find FFDs to communicate and get associated with. That is the way the remote devices let the FFDs know to add them to the routing tables.